Carrier telegraph system



Dec 25,1934.

R. E. SMITH CARRIER TELEGRAPH SYSTEM Filed Sept. 6, 1930 4 Sheets-sheet 2 HPF LPF

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FIG. 3 INVENTOR nomwsu. SMITH BY z vzam 94 W ATTORNEY Patented Dec. 25, 1934 UNITED STATES 1,985,430 CARRIER TELEGRAPH SYSTEM Rothwell E. Smith, Westfield, .N.,J.,.assignor ,to.

International Communications Laboratories,

Inc., New York, N. Y., a corporation 'of New York Application September 6, 1930, Serial No. 480,130

9 Claims.

This invention relates to electric wave transnnssion systems and more particularly to carrier wave systems utilizing a plurality of signal more commonly employed for the transmission of carrier telephone or telegraph signals. Accordingly, I have shown my invention applied to systems of this' kind; but it is by no means limited to such systems.

An important feature of this invention relates to the reduction in the number of amplifiers utilized in the system and also in the number of repeater points required, so that a large geographical distance is spannedwith an economy of apparatus. v

;In four-wire carrier systems as heretofore commonly constructed a number of repeater or amplifier circuits were inserted at a number of points along each pair of conductors, the repeater circuitson one-pair of lines or conductors being arranged to transmit the signalsin one direction and the repeater circuits of the other pair of conductors being adapted to transmit'the signals in the opposite direction. Itis an object of the present invention to provide in a fourwire system of the character described a repeat.- er circuit common to both pairs of line wires and adapted. to transmit the signals with as much efficiency in one directionas inthe other.

Another valuablefeature-ofthis invention re,-v sides in improved means for preventing singing of the repeating elements. Preferably, the singing path is not confined to the local repeater circuit but includes the'connecting lines, with their attenuating efiects. 1

Another feature relates to the reduction. of cross-talk or interference effects between paths of transmission, the'construction and arrangement being preferably such that a plurality of successive repeater circuits, adapted to alter the relation of. the transmission paths through the system are connected to the line wires.

Other objects and advantages of this invention, together with certain details ofconstruction and combinations of parts, will be described in the specification and pointed out in the appended claims.

In the drawings, Figure showingan arrangement this invention,

1 is a schematic view of c r u ts embody Fig. 2 is 'a diagrammatic view illustrating the transmission paths of the frequency groups through the system, i

Fig. 3 is a circuit diagram of the fundamental repeater circuit used in my improved transmission system, i i i Figs; 4, 5 and 6 are diagrammatic views of modified repeater circuit arrangements,

Fig. '7 is a schematic View showing a modifica tion of my invention wherein a more economical use of the frequency range transmission over. each pair of wires, and

Fig. '8 is a schematic view of ajmodified form of my invention employing. repeater amplifier circuits for separate channels of transmission.

Referring to Figs. 1, are utilized forftransmission over the paths 9 and 10formed by the two pairs of wires A and B. The. carrier currents are grouped according to their frequencies; those of a lower group being arbitrarily used for transmission, say, from west to east and frequencies of a higher group being used for transmission from east to west. It will be understood that the system will operate just as efficientlyiif the directions of transmission are reversed with respect to these groups of fre-j quencies. I

The four wire circuit consists of two pairs of linepwires A and B which are bridged by a number of repeater circuits C, D, Eat different places along said lines. Each repeater circuit, asis shown in Fig. 3, comprises an upper branch 11 and a lower branch12 each including one-way selective means for each of the frequency groups. Each selective means includes frequency selecting filters which direct the currentsthrough the proper paths. A single one-way amplifier 13 of any well-known type, such as an electron tube, isemployed in'common with both'branchesof repeater circuit C. "Similarly common amplifiers 14 and "15 connect the branches of "repeater circuits D and E respectively.

The upper branch of repeater C (Fig. 3) .includesa" low pass input filter 16 designed to pass frequencies of the lower group transmitted, say, from thewest to east, and a high pass input filter-1'7 is adapted to pass the frequencies of the higher group transmitted from the east towest. The lower branch also includes means for directing the currents of .each frequency group through the proper paths, comprising a high pass output filter 18 and a low pass output filter 19. The common amplifier 13 has its input circuit coupled by-means of transformer 20 to the upper branch of the repeater at a point intermediate may be made for l5 2 and 3, carrier "currents the low pass and high pass input filters, while transformer 21 similarly couples the output circuit of the amplifier to the lower branch of the repeater.

Currents of different frequencies transmitted over open wire or cable pairs are attenuated at different rates, the magnitude of the attenuation varying as a function of the frequency, so'-that the higher the frequency the greater the attenuation. Amplifiers normally have a uniform gainfrequency characteristic; therefore, in order to amplify the attenuated currents of the different frequencies equivalent to the amount that they are attenuated, it is necessary to provide some form of compensating network in the repeater. Accordingly, there may be connected in circuit before the amplifier and in tandem therewith a network 22 designed to make thegain-slope of the repeater circuit over the frequency groups approximately equivalent to the attenuation-slope of the lines. This network is commonly called an attenuation equalizer and may be of any well-known type.

As noted above, the common practice in fourwire systems is to arrange the repeater amplifiers in such a manner that each successive amplifier is connected so that itwill always direct the transmission of the signal currents in the same direction along one pair of wires. According to the present invention, however, the repeaters are so arranged that the amplifier of successive repeaters is reversed with respect to the preceding one. As is shown in Fig. 1, amplifier 13 is arranged to transmit the frequency groups from the upper branch to the lower one, whereas amplifier 14 transmits the frequency groups in the opposite direction or from the lower branch to the upper branch of the repeater. The arrangement of the filters is also reversed, the high pass and low pass output filters 23and 24, respectively, being in the upper branch of the repeater D andthe low pass input filter 25 and the high pass input filter 26 being in the lower branch. In repeater circuit E, the arrangement of the amplifier'l5 and the filters 27, 28, 29 and 30 is similar to the corresponding elements in repeater circuit C.

By-the construction above-outlined, currents incoming from the west over line wires A pass through the low pass input filter 16 and are amplified in the common amplifier 13. Currents of this particular group of frequencies appearing in the output of the amplifier are passed through the low pass output filter19 and are transmitted over the line wires B to the succeeding repeater circuit D wherethe group of frequencies pass through low pass input filter 25 and are again amplified byv means of common amplifier 14. The group of frequencies appearing in the output of amplifier 14 pass through the low pass output filter 24 and are transmitted over the line wires Ato the repeater circuit E where the group of frequencies passes throughthe low pass input filter 27, and are again amplified by means of common amplifier 15. The group of frequencies appearing in the output of amplifier 15 is passed throughthe low pass output filter 30 and is transmittedover the line wires B to the east terminal apparatus or an adjacent repeater, as the case may be. I

The currents comprised'in the upper groups of frequencies incoming from the east pass through the high pass filters 28, 29,26, 23, 17, 18 and alternate sections of the line wires A and B.

These currents are amplified in the common amplifiers 15, 14 and 13.

It will be seen from the above that the respective transmission paths provided for the signalling currents of the two frequency groups will be transposed through the system at each repeater from one pair of wires to the other, and cross-talk andinterference effects are reduced between the paths of transmission in the two directions.

In Fig. 2 there is shown the paths of transmission of the carrier currents through the system, thesolid line F-F' designating the path of the currents from west to east and the broken line G--G showing the path of the currents from east to west.

In multiplex carrier wave systems as heretofore designed, the singing paths were confined almost wholly to the local repeater circuits. Hence. a considerable amount of loss in the suppression region of the filters was required. In the construction outlined above, the singing path is not so localized, but includes the attenuation effects of the line sections interconnecting successive repeater circuits. It will thus be seen that more economical filters may be used in the repeater circuits.

Fig. 4 illustrates a modification of the fundamental repeater circuit shown in Fig. 3. In this modified construction the characteristics of the low pass and high pass filters are so designed as to overlap at the cut-off point. Such a filter design allows a particular frequency band, due to this overlapping, to be transmitted from line section 31 to line section 32 and in the same manner from line section 33 to line section 34. In order to prevent this band of frequencies from entering the amplifier 35, a band elimination filter 36 adapted to suppress this band of frequencies is connected to the input of the amplifier. A similar band filter 37 is inserted in the output circuit of the amplifier to prevent admission thereto of the aforesaid particular band of frequencies passing from line 33 to line 34. This filter 3'7 prevents this band of frequencies which is being passed from line section 33 to line section 34, from intermodulating with the other frequencies operating through the amplifier 35 and filters 16 and 19 for one direction, and the amplifier and filters 17 and 18 for the opposite direction. This arrangement is such that it essentially permits by-passing certain bands of frequencies around either the input or output sides of the repeater.

It will be understood that the entire transmission system may be made up of any number of repeaters. Fig. 1 indicates only the use of three repeaters shown at 13, 14 and 15, located at various points along the lines from one end to the other. The cross-talk or interference from the pairof wires A into the pair of wires B, for example, at any place in the system, will be confined to the section where it occurs between the repeaters at the ends of that section. For example, when cross-talk occurs from the line wires B to the line wires A in the section between the repeaters 13 and 14, some of the signal energy in the line wires B will be transferred to the line wires A. This transferred signal energy, being at a lower frequency than that in the line wires A, will be stopped by the high pass filters l7 and 23 in that section. Similarly, any signal energy transferred in the same way from the line wires A to the line wires B in the same section, being of a higher frequency will be stopped by the low pass filters 19 and 25. Hence, there will be no cross-talk that can be heard at either occurs; This is a decided advantage over'the' present conditions prevailing in four-wire systems where the cross-talk originating inthemrious sections of the system adds together to producegreater disturbing efiects at the terminals. 1 In Fig. 5 there is shownthe fundamental repeater circuit modified in order to take care of a conditionwhere high gain froma repeater circuit is desirable in order'to permit amplificationof the attenuated currents over "greater distanoesfor-t-he same original energy output. in this arrangement, an individual amplifier 38" is connected'between the low pass input filter 39 and the bridge point to the common amplifier 40. Between the output of the amplifier 38 and the bridge point tothe common amplifier 40 is connected another low pass filter 41 having characteristics similar to those of filter 39.- Similarly, an individual'amplifier 42- is-connected between the high pass input'filter 43 and the bridge point of theinput of the commonamplifier 40 and a filter 44 having characteristics similar to filter 43 is connected between output of the amplifier 42 and the bridge point of the input of the amplifier 40. I

Referring to Fig. 6, I have shown an arrangement which-is adapted for use where higher energy levels are desiredto be transmitted from the output of the repeater. An individual highpower amplifier 45 is interconnected between-the high pass output filter 46 and the bridge point to the output of the common amplifier 4'7 and a high-power individual amplifier 48 is connected between the low pass output filter 49 and the bridge point to the output of the amplifier 4'7. Between saidbridge point and the inputs the individual amplifiers are connected, the filters 50 and 51 having characteristics similar to the filters 46- and 49, respectively.

While the repeater circuits above described; are two-way four wire repeater circuits, they do not permit of full utilization of the frequency range which it is possible to transmit over theactual line wires. In Fig. 7-; I have shown a modified arrangement'of my inventionto afford this full utilization. For the purpose of facilitating description, arbitrary frequency groups will be assumed. From line wires 52 frequencies from zero to five kilocycles are selected by means of a low pass input filter 53 and directed through the common amplifier 54 and out through a low pass output filter 55 to line wires 56 in the west to east direction. At the same time a frequency group of six to ten kilocycles maybe transmitted from line wire 5'7 through the high pass input filter 58 through the common amplifier 54, amplified thereby, and transmitted through its high pass output filter 59 and onto line wires 60 in the east to west direction. In the same manner, the oppositely directed frequency group of zero to five kilocycles is selected from line wires 60 by means of a lowpass input filter 61 and directed through the common amplifier 62, amplified and directed through low pass output filter 63 onto line wires 5'7 in the west to east direction. 7 Similarly, the frequency group of six to ten kilocycles is taken from line wires 56, passed through a high pass input filter 64, amplified in common amplifier 62 and directed through the high pass output filter 65 onto line wires 52. It will readily be seen that by choosing frequency, groups and properly relating the same, it is possible to use the linewires 52, 5'7, 60 and-56in both' directions fromqth'e repeater at maximum efficiency with regard to frequency allocations and without any interaction between the transmission paths of the various frequency groups. This result is made possiblefby the local circuit containing the parts 61' and 64', and the local circuit of the parts 63 and 65, said circuits being connected 'by the amplifier 62. It will be notedthat this two-way four wire repeater circuit is so arranged that the transmission groups of the same frequency on adjacent wires are always transmitted: in the same direction. This-modification is connected into the carrier wave system in the same manner as shown in Fig. 1 andthe same transpositions from the standpoint of cross-talk relations obtain.

In Fig. 8 there is illustrated another modificationwhich is essentially anexpansion of the arrangement set forth in Fig. 7.". In this arrangement the transmission paths of the frequency groupsare similar. to those of Fig. '7. The selecting circuits designated .by reference numerals 66, 67,68, 69, '70, '71, 72 and 73 are preferably ofband pass filter design, the filters designated by the samereference numeral having the same characteristics. All the, filters have similar characteristics-except that. each pair is adapted to pass bands of. frequencies different from those which are selected by each of. the otherpairs; The band widths may be of a, magnitude suchas to suit a single channel or a group of channels at the sendingand receiving terminals.

Withthearrangement, shown in Fig.7, a givenband: of: frequencies can be sent over the two lines in the same. direction; and a second hand over the two lines in the opposite direction. Ehe combination of Fig. 8 will allow'two or more sepa-' rated bands. of frequenciesto be sent" over each line. in one. direction; and two-or'moreseparated bands distinct from the. first bands: to be sent in the. opposite direction over each of the two lines 9. and 10..

It will be. understood that' by substituting coupleditu'ned circuits: for the filters, .my. invention may be applied to. this type of. signal'transmiss1on....;. i I

It will also be understood that this invention is applicable to not only open wires but also to concentric core conductors and to four-wire operation over cable conductors, either within the same cable or two separate cables where all pairs within one cable are used fortransmission in one direction and the pairs of the other cable are used for transmission in the opposite direction.

What is claimed is:

1. In a carrier wave system having two twowire line circuits with repeaters connected therein, the method of transmission thereover which consists in transmitting two waves representing different frequency channels in opposite directions over separate paths along said line circuits, interchanging said paths along and on said line circuits at each repeater, amplifying said oppositely directed waves during passage thereof from one to the other of said line circuits, and separating and directing said amplified waves in opposite directions therefrom along said line circuits according to the respective frequencies thereof.

2. In a carrier wave system havinga plurality of transmission lines, the method of transmission which consists in transmitting a group of waves of given frequencies by means of one pair of lines, and a group of waves of different frequencies by means of another pair of lines, passing said groups of .waves through a common amplifier and transposing said groups of waves from the one pair of lines to the other pair at saidamplifier 3. In a carrier wave system having a plurality of transmission lines, the method of transmission which consists in transmitting a group of'waves of given frequencies by means of one pair. of-lines, and a group ofwaves of difierent frequencies over another pair of lines, passing said groups of waves through a plurality of amplifiers spaced along said lines for altering the relative positions of said groups along said lines.

4. Ina carrier wave system, the combination of a plurality of transmission lines each extending between the same two points, means for crossconnecting said transmission lines at intervals along the length thereof thereby dividing each line into a plurality of line sections, and means in each line section for confining thereto crosstalk induced therein from the corresponding section of the adjacent line.

5. In a carrier wave system, a plurality of transmission lines for transmitting signals located in difi'erentfrequency groups over a plurality of transmission paths, amplifiers connected across said lines and thereby dividing said lines into sections, and means for confining signals of one frequency group to a single transmission path.

6. A carrier wave'system wherein transmissions of two waves representing different frequency channels are oppositely directed, comprising two two-wire line circuits divided into sections, means for providing a separate transmission path along said line circuits for each wave, each transmission path being independent of the other and including a section of one line circuit and the succeeding section of the other line circuit, a common path between the two line circuits at each section division point over each of which common paths transmission of said two waves is in the same direction, said means and said common paths operating to cause transmission over the two line circuits in the same section to be in opposite directions, and transmission over adjacent sections of each line circuit to be in opposite directions.

'7. -A carrier wave transmission system according to claim 6, having an amplifier connected in each common path with its input coupled to one line circuit and its output coupled to the other line circuit, the amplifier at one section division point being reversely connected to the line circuits with respect to the connection of the preceding and succeeding amplifiers to said line circuits..

BIA carrier wave system wherein two waves representing different frequency channels are transmitted in opposite directions, comprising two two-wire line circuits divided into sections, means including wave filters at each section division point connected in said line circuits for providing a separate transmission path along said line circuits for each Wave, each transmission path being independent'of the other and including a section of one line circuit and the succeeding section of the other line circuit, a common path including an amplifier for both waves connecting the two line circuits at each section division point, said filters and said common path at each section division point co-operating to cause transmission of one wave in one direction over one line circuit and transmission of the other wave in the opposite direction over the other line circuit in the same section and to cause transmission of said one wave over the other line circuit in the succeeding section in a direction opposite to the direction of transmission of said other wave over said one line circuit in said succeeding section.

, 9. .Aiour-wire signal transmission system comprising two two-wire line circuits extending through a repeater station thereby dividing each circuit into east and west line sections, low pass filters at the repeater station connected one in the east section of one line circuit and the other in the west section of the other line circuit, high pass filters at the repeater station connected one in the west section of said one line circuit and the other in the east section of said other line circuit, and an amplifier at the repeater station for amplifying simultaneously both high and low frequencies having the'input connected to one line circuit at a point between the filters therein and the output thereof connected to the other line circuit at a point between the filters therein.

ROTHWELL E. SMITH. 

